For VS Quake I use QuakeWorld.
You should be able to join the QuakeWorld server from any QuakeWorld client. I use FodQuake, personally. Put your /id, /hipnotic, and /rogue folders into whatever QuakeWorld client you choose. To connect to the server either find it in the server list. Connecting directly doesn't seem to work unless you find the ip address. You can find it at https://www.quakeservers.net/lists/north_america/servers.txt
For COOP I use DarkPlaces, as original NetQuake networking code didn't play nicely with my router setup. Same thing, plop /id, /hipnotic, and /rogue into the darkplaces base folder, but you also need to run the client with the same expansion that the server is using - or you won't see it in the server list. So if the server is using running Dissolution of Eternity (rogue), for example, you need to run your client with the command line "-rogue". Else, you'll spawn in the wrong place, or level, or whatever, if you direct connect.
Join through the server browser or direct connect at clovr.xyz
ATM, only running the original game and it's expansions in COOP.